The recent emergence of smartphones has led to a sharp increase in Transport Control Protocol (TCP)-based packet exchanges between User Equipments (UEs) and the Internet/network. The TCP is generally used to transmit traffic requiring reliability or to transmit traffic requiring flow control over the Internet. The TCP operates based on an end-to-end session and a TCP session is generated by end-to-end handshaking. If an on-going TCP session is not used for a predetermined time, the TCP session is released. There are various types of TCP-based service applications. Among the TCP-based service applications, for example, a messenger and chatting service such as Kakao Talk™ or Google Talk™ often transmits a keep-alive message to a server even in the absence of valid transmission data in order to prevent release of a TCP session.
For periodic transmission of a keep-alive message, a UE switches from idle mode to connected mode in spite of the absence of valid data. The state switching operation imposes a signaling/processing load on the network and the periodic transmission of a keep-alive message consumes battery power of the UE. Accordingly, there is a need for a method for effectively keeping a TCP session alive.